This invention relates generally to power transmission elements such as gears, pulleys, sheaves and sprockets and, more particularly, to thermoplastic power transmission elements mountable on a keyed driven shaft.
The use of thermoplastic materials in the manufacture of power transmission elements such as gears, pulleys, sheaves and sprockets greatly reduces manufacturing costs and provides tremendous savings over similar parts made of metal. One particular drawback of this practice, however, is that plastics have considerably lower shear and torsional strengths than most metals.
In power transmission elements, such as gears, pulleys, sheaves and sprockets that are driven from a keyed shaft, the keyway is subject to severe stress and strain during operation. In plastic components, keyway strength is often the ultimate limiting factor in defining the maximum capacity of the power transmission element.
Keyway failure in plastic power transmission elements results from a number of factors including increased notch sensitivity, creep and the reduced impact resistance and rigidity of thermoplastic materials. One common technique for increasing keyway strength in plastic elements is to increase the hub and keyway length. This, however, results in a larger component and is not always a practical solution.